Ion beams, or streams of ions, are used and have been used: to etch materials; to clean substrates for subsequent laying down (coating) of materials thereon; to effect sputtering to provide the material to be laid down; to alter the properties of films as deposited by other sources; and to effect chemical reactions between certain gases and the material bombarded by the ion stream. All of these many practices have required an ion beam source or a source of a stream of ions. In the prior art, ion beam guns have been of varied designs. One popular design has been to employ a cylindrical stainless steel anode which has cathode end pieces. The cathode and anode are, of course, electrically insulated from one another and when electrical power is applied to the cathode and anode there is an electrostatic field created therebetween. Ionizable gas is fed to the cylinder and reacts to provide a glow discharge and a source of ions.
In the prior art ion beam guns, magnetic flux is generated by locating a winding around the circumference of the cylinder and passing an electrical current therethrough. The magnetic flux thus generated passes through the stainless steel cylinder and acts in conjunction with the electrostatic field to cause ions to move along a substantially helical path toward the cathode, i.e., end pieces and through an aperture in the end pieces. A major problem with such prior art ion beam guns lies in the fact that they have been physically large to accommodate the windings for the electromagnetic sources of flux, i.e., solenoid type devices. Very often such prior art devices have employed high temperature filaments within the plasma chamber to be heated up and provide electrons which in turn move about in the chamber to have collisions and free up ions thereby increasing the density of the plasma. However, such filaments necessitate a relatively large device with added power sources and necessitate regular maintenance to replace burned out filaments. In addition, the high temperature filament ion guns generate unwanted heat. In addition, the configuration and densities of the electrostatic fields and the magnetic flux fields of the prior art ion beam guns have not enhanced the plasma density to provide high output ion currents at relatively low source chamber pressures. The present invention employs an inverted magnetron arrangement with the cathode being coaxial with the anode, with the magnetic flux being coaxial with the cathode and anode, with the exit aperture being intermediate with the ends of the chamber, and with an electrostatic focusing device at the exit aperture, all of which permits a physically smaller ion gun to be assembled and which permits a greater output of ions, i.e., a greater ion current at lower chamber pressure.